Honestly we don't know if people are born with depression or not. We don't know what biochemically causes depression in the first place. Very young children can have depression and attempt suicide (I was one of them). And asserting that depression is curable is suspicious too because, sure, it is for most people - most cases will resolve over time with or without effective treatment - but there's a whole population of treatment resistant chronic depressives that have terrible outcomes and single-digit rates of remission. I don't think we understand nearly enough about the condition to put all depressed people in the "curable temporary illness" category.